I made that mistake myself a few weeks ago thinking the same but a user corrected me in saying that self-made Legendaries are those users that reach Legendary rank from Newbie rank.
I knew it, but I still would prefer to use the name-calling, self-made, because I think we should not make things become overcomplicated like this. Self-made, half-self-made, and so forth. Basically, the implications behind the self-made name-calling is to disclose that such users have made good contributions in the forum, and they received enough merits to move up from lower ranks to higher ranks. That's all. There is LoyceV, whom received nearly 3000 Merits till now. LoyceV is clearly not a self-made Legendary, but probably worths more than most of upcoming self-made Legendary users.